Air Pressure Origins
What are most differences in air pressure caused by?
The earth's atmosphere is affected by many interacting effects. Here are a
few: 1. Sunlight, which warms one side of the planet vs. the other. 2.
Cloud cover that depends upon many of the other effects. 3. The tilt of the
earth which simply put regulates summer as opposed to winter. 4. Tides,
which are affected by the position of the Moon in relation to the earth and
sun. And this is just a short list!! All of these factors interact in a
complex way -- that is why weather is difficult to predict. The net effect
is that the amount of air at one location above the earth changes from
season, day/night, temperature and so on. The more air that is above a
particular location the greater is the air pressure, but the details are
Air pressure reflects the amount of air above you in the atmosphere;
the pressure is a measure of the weight of the air above you.
Meteorologists speak of a kind of fictitious "air column" as being
So, in a High pressure area there is more air above you than
there is in a Low pressure area.
Low pressure weather systems can add to the amount of air
in the air column outside of them to create High pressure areas;
one example of this is that Low pressure storm systems cause
air to be raised high into the atmosphere; that air spills out
around and well away from the center of the Low, adding weight
to the air column in the surrounding high pressure areas.
The converse of that is that Low pressure systems have low
pressure because they are ejecting air up and out from them,
thereby reducing the amount of air in the air column in their
David R. Cook
Climate Research Section
Environmental Science Division
Update: June 2012